Method for de-icing a device for separating air by cryogenic distillation and device adapted to be de-iced using this method

ABSTRACT

Method for separating air by cryogenic distillation in an air separation device comprising a system of columns, a first turbine and a second turbine, wherein, in de-icing operation, a common duct bringing air from the two turbines to a column is closed by means of an isolation valve, a purge gas is sent to the turbines at a temperature above 0° C. in order to de-ice them, but purge gas is not sent to the system of columns.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to French patent application No. FR1757493, filed Aug. 3, 2017, French patent application No. FR1757495, filed Aug. 3, 2017, French patent application No. FR1757497, filed Aug. 3, 2017, and French patent application No. FR1757498, filed Aug. 3, 2017, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method for de-icing a device for separating air by cryogenic distillation and to a device adapted to be de-iced using this method.

BACKGROUND

A device for separating air by cryogenic distillation must be regularly de-iced in order to purge carbon dioxide, water and hydrocarbons that could have accumulated in the device.

To this end, according to a long-established method, the device needs to be heated to a temperature above 0° C.

Firstly, liquid that has accumulated in the device is purged and then supply air passes through the device, with the one or more cold production turbine(s) being shut down. The pressure in the device increases and the accumulated gases are released into the atmosphere.

In order to reheat a turbine, the air inlet and outlet to the turbine are closed using a valve at the inlet and a valve at the outlet and a gas is sent to the turbine by passing through the discharge towards the inlet (or optionally by passing from the inlet to the outlet).

Manual isolation valves are provided at the inlet and the outlet of each machine. These valves are not necessarily shown in the simplified drawings of a separation device illustrating its normal operation to avoid overcomplicating the drawing.

Once the device is de-iced, it can be restarted by sending air to the one or more turbine(s) by cooling the device.

SUMMARY OF THE INVENTION

The aim of certain embodiments of the present invention is to reduce the time required for de-icing and/or restarting and optionally to reduce the operating time of a backup vaporiser for supplying a client. By using certain embodiments of the present invention, it is no longer necessary for the columns to be purged in order to remove the liquid that they contain.

Furthermore, a valve no longer needs to be provided at the outlet of each turbine, therefore the total number of valves is reduced.

According to one aim of the invention, a device is provided for separating air by cryogenic distillation, comprising a system of columns, a first turbine, a second turbine, optionally a first compressor coupled to the first turbine, optionally a second compressor coupled to the second turbine, a heat exchanger, means for sending at least one first fraction of air cooled in the heat exchanger at an intermediate temperature thereof to the first and the second turbines, a first expanded air duct connected to the backflow of the first turbine and to the system of columns, a second expanded air duct connected to the backflow of the second turbine, a common duct connected to the first and second ducts to bring the expanded air of the turbines to a column of the system of columns and an isolation valve, preferably a single isolation valve, allowing the common duct to be closed.

According to other optional aspects:

-   -   the device comprises a short-circuiting duct connecting the         inlet of the first turbine to the outlet of the first turbine as         well as to the common duct at a position upstream of the         isolation valve, allowing air to pass from the inlet of the         first turbine to the common duct, without passing through a         turbine;     -   the device comprises at least one compressor driven by one of         the first and second turbines;     -   the device comprises means for sending air from the compressor         driven by one of the turbines to the turbines after cooling in         the heat exchanger or to the heat exchanger in order to be at         least partly liquefied therein;     -   the device comprises a venting valve upstream of the isolation         valve and downstream of the first and second turbines,         preferably downstream of the short-circuiting duct;     -   the isolation valve is the only valve connecting the outlet of         the first turbine to the system of columns and/or connecting the         outlet of the second turbine to the system of columns to allow         the passage of air therein.

According to another aim of the invention, a method is provided for separating air by cryogenic distillation in an air separation device comprising a system of columns, a first turbine, a second turbine, optionally a first compressor coupled to the first turbine, optionally a second compressor coupled to the second turbine and a heat exchanger, wherein:

i) in normal operation, at least one first fraction of air is sent to cool in the heat exchanger at an intermediate temperature thereof and is subsequently sent to the first and the second turbines, air allowed to expand in the first turbine and air allowed to expand in the second turbine is sent to a column of the system of columns through a common duct, the air originating from the common duct is separated in the system of columns in order to produce at least one nitrogen or oxygen enriched fluid; and

ii) in de-icing operation, the common duct is closed by means of an isolation valve, a purge gas is sent to the turbines at a temperature above 0° C. in order to de-ice them, but purge gas is not sent to the system of columns.

Optionally:

-   -   the common duct is closed by means of the isolation valve, which         is the only valve to be closed to this end;     -   the isolation valve is closed manually;     -   the common duct is connected to the column of the system of         columns operating at the highest pressure;     -   de-icing is performed by sending dry air to the inlet of the         first compressor;     -   de-icing is performed by sending a dry gas in the opposite         direction to the air in normal operation;     -   the method does not comprise a step of purging columns during         de-icing operation.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.

The invention will be described in further detail with reference to the FIGURE, which shows a device for separating air by cryogenic distillation according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The device comprises a system of columns comprising a column operating at a first pressure K1 and a column operating at a second pressure K2 below the first pressure. The columns are thermally connected through a bottom reboiler of the second column heated by nitrogen from the top of the first column. Liquid oxygen 31 is extracted from the bottom of the second column K2 and gaseous nitrogen 33 is extracted from the top of the second column. Liquid nitrogen is sent from the top of the second column in certain phases in order to help to keep the process cold.

The device comprises a first air expansion turbine T1, a second air expansion turbine T2, a first air compressor C1 coupled to the first turbine and a second air compressor C2 coupled to the second turbine. The compressed air 1 is divided into two fractions, including a first fraction 3 in the heat exchanger E. A second fraction 5 is sent to the first compressor C1, where it is compressed at a pressure above the pressure of the first fraction. The outlet of the first compressor C1 is connected to the inlet of said compressor through a valve V8.

According to a first variation, the first fraction 3 is output from a heat exchanger at an intermediate temperature thereof and, having not been compressed in the first compressor, is sent to the first and the second turbines.

The second fraction 5 cools in the heat exchanger to an intermediate temperature thereof, after having been compressed in the first compressor. It is subsequently sent to the second compressor C2.

During normal operation, air from the first and second turbines is sent to the first column K1 in order to be separated through the single valve V11 and the duct 13. The second fraction 5 is compressed in the second compressor C2 and is subsequently cooled in the heat exchanger before being sent in liquid form to the first column K1 through the valve V9. The valves V2 and V3 are closed. Optionally, part of the air can be sent to the section via the short-circuiting duct 15 that connects the inlet of the turbine T1 upstream of a valve V13 to the duct 13 upstream of the valve V11. The short-circuiting duct 15 comprises a valve V7 but no turbine. Any flow arriving from a turbine and optionally the short-circuiting duct must pass through the valve V11, with no valve being connected between the turbine outlets and the valve V11.

For de-icing, the isolation valve V11 is closed to prevent the arrival of fluids originating from the column K1 during the reheating thereof, which can cause an accident. In order to de-ice the turbines, a dry gas is sent into each turbine, passing in the opposite direction to the normal passage of the air to be distilled. The valves V4 and V5 can be closed or opened as a function of the upstream or downstream location of the outlet or optionally of the de-icing inlet for the considered turbine.

The manual isolation valve V11 is disposed at the outlet of the turbines T1, T2. The short-circuiting duct 15 is connected at a point upstream of the valve V11 and downstream of the air intakes of the turbines T1, T2. With this valve V11, as well as the liquid air valve V9, being closed, it allows the machines to be isolated from the column and thus allows the liquids to be retained in the columns.

The lack of valves directly downstream of the discharges of the turbines T1, T2 is to be noted, the single valve V11 was placed downstream of the air intake of the two turbines and of the short-circuiting air of the duct 15.

Thus, by closing the valve V11 manually, it is possible to prevent cold gas from returning from the column (due to its reheating) to the turbines or the compressors.

This saves restarting time and limits the operating time of the backup vaporisation when changing a cartridge in the machines.

A valve S1 is connected to the outlet of the turbine T1 upstream of the valve V11 and the air intake points of the turbine T2 and of the short-circuiting duct 15.

An injection of dry gas, preferably of air at the inlet of the cold booster C1, in order to prevent cold migration from the exchange line E, allows ease of replacement of the turbine T1 cartridge, without having to de-ice the exchange line E.

This also saves restarting time and limits the operating time for vaporising liquid products of the device when changing a machine cartridge.

While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.

“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited. 

1. A device for separating air by cryogenic distillation, comprising a system of columns, a first turbine, a second turbine, a heat exchanger, means for sending at least one first fraction of air cooled in the heat exchanger at an intermediate temperature thereof to the first and the second turbines, a first expanded air duct connected to the backflow of the first turbine and to the system of columns, a second expanded air duct connected to the backflow of the second turbine, a common duct connected to the first and second ducts to bring the expanded air of the turbines to a column of the system of columns and an isolation valve, preferably a single isolation valve, allowing the common duct to be closed.
 2. The device according to claim 1, further comprising a first compressor coupled to the first turbine; and a second compressor coupled to the second turbine
 3. The device according to claim 1, further comprising a short-circuiting duct connecting the inlet of the first turbine to the outlet of the first turbine as well as to the common duct at a position upstream of the isolation valve, allowing air to pass from the inlet of the first turbine to the common duct, without passing through a turbine.
 4. The device according to claim 1, further comprising at least one compressor driven by one of the first and second turbines.
 5. The device according to claim 4, further comprising means for sending air from the compressor driven by one of the turbines to the turbines after cooling in the heat exchanger or to the heat exchanger in order to be at least partly liquefied therein.
 6. The device according to claim 1, further comprising a venting valve upstream of the isolation valve and downstream of the first and second turbines, preferably downstream of the short-circuiting duct.
 7. The device according to claim 1, wherein the isolation valve is the only valve connecting the outlet of the first turbine to the system of columns and/or connecting the outlet of the second turbine to the system of columns to allow air to enter the system.
 8. A method for separating air by cryogenic distillation in an air separation device comprising a system of columns, a first turbine, a second turbine, and a heat exchanger, wherein: i) in a normal operation, at least one first fraction of air is sent to cool in the heat exchanger at an intermediate temperature thereof and is subsequently sent to the first and the second turbines, air allowed to expand in the first turbine and air allowed to expand in the second turbine is sent to a column of the system of columns through a common duct, the air originating from the common duct is separated in the system of columns in order to produce at least one nitrogen or oxygen enriched fluid; and ii) in a de-icing operation, the common duct is closed by means of an isolation valve, a purge gas is sent to the turbines at a temperature above 0° C. in order to de-ice them, but purge gas is not sent to the system of columns.
 9. The method according to claim 8, wherein the common duct is closed by means of the isolation valve, which is the only valve to be closed to this end.
 10. The method according to claim 8, wherein the air separation device further comprises a first compressor coupled to the first turbine, optionally a second compressor coupled to the second turbine.
 11. The method according to claim 8, wherein the isolation valve is closed manually.
 12. The method according to claim 8, wherein the common duct is connected to the column of the system of columns operating at the highest pressure.
 13. The method according to claim 8, wherein de-icing is performed by sending dry air to the inlet of the first compressor.
 14. The method according to claim 8, wherein de-icing is performed by sending a dry gas in the opposite direction to the air in normal operation.
 15. The method according to claim 8, further comprising the absence of a step of purging columns during the de-icing operation. 